Remove unnecessary puts statement in Rakefile
Fix OperatingSystem determine method to operator on a class-level
Add initial support for libgit2/rugged involving massive changes

Large change set here! Difficult to split this up into modular changes
as Grit at the time was the heart of the processing. The initial
implementation done here for Rugged works, and all the specs are
currently passing.

The GPG signing issue is no longer an issue, and Rugged also provides
a substantial speed boost and memory reduction than the Grit
implementation. The current state also run on Ruby 2.0.x as we are not
held back by Grit.

Remove:
 * The use of Grit for git processing
 * repo.rb as Rugged::Repository provided sufficient repo finding
   capabilities
 * Mixin for Grit::Blob to include LanguageSniffer functionality
 * blob_finder.rb as Rugged::Diff::Patch provides sufficient
   functionality to acquire the individual SHA's of blobs affected in
   the diff, which then can be Rugged::Repository.lookup(sha)
 * FileSummary struct and instead just use the patch information from
   DiffSummary

Add:
 * Rugged for git processing
 * Direct use of LanguageSniffer in diff_summary to detect the language
   of the diff's content (using the blob in question)
 * Additional functionality to diff_summary.rb as it now is responsible
   for working with patches (provides #additions, #deletions, #status)
 * Additional information on LanguageSummary (:added_files,
   :deleted_files, :modified_files)

Refactor:
 * How we found the commits to process, Grit::Commit.find_all(…) was
   replaces with Rugged::Walker
 * spec_helper.rb to now use Rugged::Repository instead of our own class
 * The terminology of :create, :delete to :added_files, :deleted_files

Fix:
 * The ability to handle time_since and time_until for commits to work
   with Rugged (check on each commit if it is valid -- #valid_commit?)
 * Specs to work with new implementation and terminologies
 * fixtures to use the updated key names
Update minimum Ruby version to 1.9.3, add travis-ci support for 2.0.0

Update:
 * gemspec's minimum Ruby version to >= 1.9.3
 * .ruby-version to use 2.0.0 (newest supported ruby version)

Remove:
 * Ruby 1.9.2 testing for travis-ci

Add:
 * Ruby 2.0.0 testing for travis-ci
Adjust branch option to specify the branch to collect statistics on

Change:
 * The function of the branch CLI flag to specify the specific branch
   we want to collect statistics on. This differs from the original
   function since we use to be able to collect all commits on a set of
   branches. Rugged only allows us to walk through from the HEAD of one
   branch at a time (we might be able to expand on this by doing
   multiple walks from the HEAD of each branch).

Refactor:
 * spec_helper to require git_statistics since it will include CLI class
   and by default it will also include the initialize file
 * The way we pass the branch into the collection method (pass it within
   the options hash)

Add:
 * Default branch constant in CLI class
Merge pull request #61 from kevinjalbert/move-to-rugged

Move from Grit to Rugged for git processing